Ballistic Supercavitating Nano Swimmer Driven by Single Gaussian Beam Optical Pushing and Pulling Forces
Directed high-speed motion of nanoscale objects in fluids (nano swimmers) can have a wide range of applications like molecular machinery, nano robotics, drug delivery, and material assembly. Here, we report ballistic plasmonic Au nanoparticle (NP) swimmers with unprecedented speeds realized by not only optical pushing but also pulling forces from a single Gaussian laser beam. Both the optical pulling and high swimmer speeds are made possible by a unique NP-laser interaction. The Au NP excited by the laser at the surface plasmon resonance peak can generate a nanoscale bubble, which can encapsulate the NP (i.e., supercavitation) to create a virtually frictionless environment for it to move, like the Leidenfrost effect. While optical forces are mostly positive, certain NP-bubble configurations can lead to negative optical forces that pull the NP to swims against the photon stream. The demonstrated ultra-fast, light-driven NP movement may benefit a wide range of nano- and bio-applications and provide new insights to the field of negative optical force.